Acrylic resins modified with alkanolamines



United States Patent ACRYLIC RESINS MODIFIED wrrn ALKANQLAMINES No Drawing. Application December 4, 1951 Serial No. 259,882

6 Claims. (Cl. 2602.1)

This invention relates to a method for removing acidic materials, such as mercaptans and hydrogen sulfide, from gas mixtures, petroleum fractions and the like and to a composition of matter useful in the process. In particular, the composition of matter comprises a resinous material having a prepared active surface of amine groups which make it reactive with hydrogen sulfide and mercaptans in an easily reversible reaction. This application is a continuation-in-part of application, Serial No. 45,584, filed August 21, 1948, now United States Patent 2,592,523.

In the conduct of many of the normal operations in the refining of crude petroleum, sulfur in the form of hydrogen sulfide and mercaptans creates complications which necessitate extra steps to make possible the smooth operation of processes employing recovered hydrocarbons. Thus, recovery of various light gases from crude oil involves their separation from hydrogen sulfide in order that the purified hydrocarbon gas can be sold. Commercial requirements for various hydrocarbon fuels, such as normal fuel oils, kerosenes and gasolines, call for the preparation of sweet products. Similarly, when hydrocarbons are to be used in various organic chemical reactions and syntheses, it is preferred that the hydrocarbon be substantially free of sulfur, because the reaction conditions to which the hydrocarbon may be subjected are such that undesirable contaminants can appear in the product. Also, because sulfur has considerable value as such, its separation is accomplished wherever possible or economically feasible.

Accordingly, it is a fundamental object of this invention to provide a process by means of which sulfur in the form of hydrogen sulfide or mercaptans, as they occur with oil, can be conveniently recovered directly from the petroleum and fractions thereof.

It is a second object of' the invention to provide a composition of matter which can enter into reversible reaction with the compounds of sulfur to be recovered.

It is a further object of the invention to provide a method and composition of matter by means of which sweetening operations can be simplified.

It is a still further object of the invention to provide a composition bymeans of which selected sulfur components of hydrocarbon fractions can be removed therefrom.

This invention, accordingly, comprises a method of carrying out a purification of certain gaseous and liquid fractions, and includes a composition of matter useful in the process.

More specifically, the composition constituting one phase of the instant invention comprises a resin of any one of several types, such as polymethyl methacrylates, polyvinyl chlorides, polyvinyl acetates, polyvinylidene chlorides, polymers formed from materials containing one or more allyl groups, or alkyd type resins, which has been modified by reaction with an organic alkanolamine or other organic nitrogen compound, so that the surface of the modified resin presents amine groups or substituted amine groups properly oriented in relation to the surface for reaction with any compound or compounds exposed thereto. When the composition is thus prepared and has an active surface of amine groups or substituted amine groups, it can enter into reversible reaction with hydrogen sulfide and mercaptans and thereby form the basis of a process for separating hydrogen sulfide and mercaptans from admixture with other gases and liquids not reactive with the modified resin.

When a modified resin is prepared in accordance with the invention and has an active surface of primary, secondary or tertiary amine groups, a gas or liquid, such as petroleum or petroleum fractions, containing hydrogen sulfide or mercaptan is passed through a tower or condenser packed with this resinous absorbent in granular form. The active surface of the exposed resin which presents primary, secondary or tertiary amine groups, preferably of the aliphatic type, to the gases and petroleum fractions flowing thereover, reacts with the hydrogen sulfide and mercaptans contained therein to permit only the hydrocarbon to escape from the vessel. When the resin has become saturated with hydrogen sulfide and mercaptan, it can be regenerated by heating to reverse the reaction between the hydrogen sulfide and the amine groups. This salt of hydrogen sulfide or mercaptan formed on the surface of the absorbent can be decomposed and the absorbent regenerated either by washing the spent absorbent and exposing it to a current of steam or inert gas, or simply by heating the salt and distilling off the hydrogen sulfide or mercaptan. The advantage of the process should be apparent from the fact that it is not necessary to remove the resin from the tower for regeneration and, because the reaction is substantially quantitatively reversible, the material may be regenerated repeatedly.

The preparation of suitable absorbents for the process may be carried out by reacting a resin containing an active group with an ethanolarnine or other suitable amines.

If the resin molecule is looked upon as a chain in which functional groups occur at intervals, the alkano-l amine or other suitable amines used to react therewith can be fastened to the resin surface through reaction of the hydroxyl portion of the molecule to leave the amine portion free for reaction, yet held to the surface through the functional portion of the resin molecule. The alkyl portion of the amine molecule may be a chain of any length. Amine groups carried by chains of as many as 25 carbon atoms are satisfactory. the amine group added to the resin be attached totlie functional portion of the resin molecule through at least about 1 or 2 carbon atoms so that it will be substantially uninfiuenced by the resin molecule. Also, the resin molecule should be sufiiciently cross-linked to avoid thermoplasticity of the composition. There are several methods of preparing suitable absorbents for use in the process which can be described as follows:

Method 1Preparati0n by the transesterification reaction..An acrylic resin, such as polymethyl methacry cool and is reduced to granular form by grinding. This material is then used as an absorbent in a tower for purie ty n pe um ct n A eaction p esent ng t e It is preferred thatformation of the modified resin can be'represented as follows:

CH; EH; I

C-CHr-- CH This material is polymeric in nature and has exposed could be linked to two separate molecules of the resin, or it could be attached to a molecule at only one end.

Method 3Preparation of the modified resin from alkyd type starting materials.-Any amine containing 2 or more hydroxy groups, such as diethanolamine, is heated with an organic acid containing two or more carboxyl groups, as, for example, adipic acid. The material will polymerize and finally will be viscous after considerable water has been eliminated in the reaction. Finally, when the polymerization has been carried out to a reasonable extent, the resin is recovered, reduced to granular or powdered form, after which it is washed with water, then with excess sodium hydroxide and finally with water to remove excess sodium hydroxide.

('n +1)HOCH:CH;NHCH2CH:OH (n DEC 00 CHiCHaCHgCH C OOH active secondary amine groups separated from the original molecule by chains of two carbon atoms, which modified resin will enter into reversible reaction with hydrogen sulfide to form a salt. The reaction is readily reversible thereby permitting regeneration of the modified resin and its re-use in an absorption reaction. Though the product has been shown as having the diethanolamine connecting two ester groups, it could be linked to two separate molecules of the resin, or it could be attached to a molecule at only one end.

Method 2--Preparation of the modified resin by a reaction of the Williamson type.If a resin containing an active halogen, such as polyvinyl chloride, polyvinyl chloride acetate or polyvinylidene chloride is to be used as the basis for the reaction, it can be reacted with the alkanolamine in aqueous or alcoholic solution thereof and sodium hydroxide. The mixture is warmed in order to complete the reaction. Finally, the resin is washed with water to reduce the inorganic chloride content, dried, reduced to granular form and used as an absorbent in a tower for purification of petroleum fractions. The reaction representing the formation of the resin is illustrated as follows:

cnoH ---cnonr The modified resin could also be formed by reacting the material with sodium cyanide to form the nitrile and then reducing the latter to the amine.

The product, it will be observed, is polymeric in nature and has an active surface of secondary amine groups exposed for reaction with hydrogen sulfide and mercaptans. This surface will enter into reversible reaction with hydrogen sulfide to form a salt. Thus, it will be seen that by packing an absorption tower with a modified resin of the type described, a process for the separation of hydrogen sulfide and mercaptans from petroleum fractions and various gases can readily be devised. Though the product has been shown as having the diethanolamine connected through two ether groups, it

' fied product.

on-cul on- 2H2- L J +nCl-CHzCOOH t A H ll It will be seen that the product formed in this reaction is polymeric in nature and will have a surface of exposed secondary amine groups available for reaction with hydrogen sulfide and mercaptans.

This reaction is reversible by means of which it is seen that the modified resin is readily recovered.

The preceding set of examples serves to illustrate that the type of modified resin contemplated for preparation in accordance with the invention is one which has amine groups attached to the functional group of the resin molecule through alkoxy chains. It is preferred that the chain be at least about one or two carbon atoms in length, because attachment of the amine directly to the resin molecule may cause it to lose some of its character as an amine and also to modify the properties of the resin. The attachment of the amine to the resin molecule through longer chains is feasible and desirable, for in such cases the basic character of the amine group is preserved. It is most convenient in preparing the modified resin to use compounds such as alkanolamines for the reaction, because they have the amine group already attached to an alkyl group and, additionally, carry a hyestee r y group eh is a ailable e reac o with resin molecule. Thus, commo'ri'alkariolamines, such asj'm no-, di-, and trietlianol and mom; di-, and triisopropanol amines can be used for reaction with the resin. It is not necessary that the amine be symmetrical, for mixed alkanolamines containing. alkyl groups having different numbers of carbon atoms, such as 'ethanolfisopropanol and ethanol-n-butanol amine can also be used. Similarly, haloalkylamines, such as Zi-QitlblOQthYltilftliflfi and 4- bromo-butyl amine, which contain one halogen atom in the alkyl group which is reactable with the resin, can be used to attach an amine group to the resin molecule. Cyanides, as pointed out, can be used for reaction with certain resins to form nitri les, which, in turn, can be reduced to the appropriate amines. Y Direct reaction of sodium cyanide with the resin to attach a nitrile group thereto can be practiced and the compound subsequently reduced to the amine. v

The modified resins just described are further convertible into quaternary ammonium hydroxide derivatives. The presence of the ua e na y. amm n um h drex e group increases e be i it endth e a et e e the abi of the modified r in in reme hydro en u i e. and m tcaptans from aqueous or hydrocarbonsolutions. To form these derivatives of the modified resins of this invention, it is only necessary to treat them with an; alkylating agent in the presence of an alkali. The reaction which takes place attaches alkyl groups to the nitroge'ns of the resin molecule, forming a quaternary ammonium ion, which associates with any negative ions present. The reaction may be accomplished. in one or two steps, as will be demonstrated. In the following equations illustrating the one and two step processes for forming these derivatives of greater basicity, the R groups represent those parts of the modified resin moleculewhich" hold the nitrogen atom. Atmospheric or. super-atmospheric pressures may be used during these reactions.

Using a modified resin with a secondary amin'e group within the molecule as an example, the following reaction with an alkylating agent, dimethyl sulfate, and alkali, such as sodium hydroxide, takes place;, i

NH 2(OHs)2SO NaOH v R\ CH:

-t I .f'e 'res t fi 'eemfi 4 a on:

Before these modified resins containing quaternary ammonium salts can be used for the removal of hydrogen sulfide or mercaptans, they must be converted to the free quaternary base by percolating alkali solution, aqueous sodium hydroxide for example, through a bed of the alkylated resin derivative. The following reaction then takes place:

The modified resins containing secondary amine groups, prepared in accordance with this invention, may be converted into resins of the quaternary ammonium hydroxide type by using other alkylating agents than dimethyl sulfate. For example, the dimethyl sulfate may be replaced by an alkyl halide, including methyl chloride, methyl bromide, methyl iodide, or many other alkylating agents may be used. Examples include diethyl sulfate, sodium methyl sulfate, sodium benzyl sulfate, and benzyl chloride.

The two-step process, above referred to, comprises reacting the modified resin with a suitable alkylating agent and alkali to form the alkylated derivative thereof. The

alkylated derivativeis then reacted with additional alkylating agent to form the quaternary ammonium salt in ac fate as the alkylating agent:

SO4CHs-l-NaOH NaS 0 0113 H1O R OH: N 50,0118. R I R/ CHa The quaternary ammonium salt thus produced can be converted into the quaternary ammonium hydroxide derivative by percolation of aqueous alkali therethrough as has been described. Where it is contemplated to use the quaternary ammonium derivatives for removal of sulfur compounds from non-aqueous fluids, as hydrocarbons, the modified resin derivative must be dried with a current of warm inert gas so that the non-aqueous fluid will wet the resin and come in contact with the active groups to effect absorption.

These quaternary ammonium hydroxide derivatives of the modified resins which have been used to absorb sulfur compounds from solutions may be regenerated by steaming or by passing aqueous alkali therethrough. Subsequent drying is only necessary if'the regenerated modified resin derivative is to be used with non-aqueous fluids.

It is apparent from the above examples and description, that the type of compound to be used for the absorption of the acidic materials from hydrocarbons and hydro- "carbon mixtures is that which has the amine group oriented outwardly from the resin molecule.

When modified resins of the types described are prepared, solid compoundsresult which can be conveniently used for the treatment of hydrocarbon materials. The problem raised by the employment of aqueous solutions for removing mercaptans and acidic materials from hydrocarbons is readily solved, because the equilibrium problems rea e y the se f a e t do no r e.- In the use of any' aqueous solution for removing acidic materials from hydrocarbons, this equilibrium problem is of considerable moment, for, more often than not, the equilibrium runs against the removal of the acidic and sulfur-containing compounds. In the instant case where a solid compound is used for reaction with the acidic materials, it can be recovered by treatment with water or aqueous alkali solutions to hydrolyze off the absorbed material.

When it is desired to prepare a modified resin product suitable for separation of hydrogen sulfide from petroleum liquids and gases, it is best to prepare a modified resin which will have a surface of secondary amine groups. The principal reasons for so doing are that the resin is a solid and it forms a salt with hydrogen sulfide which is a solid. Secondary amine groups are, in general, somewhat more basic than either primary or tertiary amine groups. When it is in this solid form, it is easily possible to recover the hydrogen sulfide with a caustic wash, by steaming it or by passing a hot gas through it.

The method of removing hydrogen sulfide and mercaptans from petroleum fractions follows readily from the above description. A resin having its surface properly modified with amine groups is reduced to granular form and employed in a tower as packing. The fluid, for example, a petroleum fraction, it is desired to strip of acidic constituents, such as hydrogen sulfide or mercaptan, is passed through the tower at ambient temperature at a rate which will permit sufficient residence time to bring about substantially complete reaction of the acidic constituent with the resin. Because the reaction of the modified resin with acidic materials begins to reverse at about 100 C., it is best to operate stripping steps at about ambient temperatures and recover the resin at temperatures above 100 C. Upon exhaustion of the absorptive power of the resin, it-is regenerated by washing with an alkali solution, about to percent aqueous sodium hydroxide, if it is desired to recover the acidic constituents as a salt. Sometimes it is desired to recover hydrogen sulfide and mercaptan as such from a petroleum fraction, in which case the exhausted resin is steamed while held at a temperature of about 100 to 300 C. Hydrogen sulfide and mercaptan are readily recovered by reversal of the addition reaction.

The general reaction for the formation of the salt of the modified resin with hydrogen sulfide or mercaptan may be represented as follows:

In the equation R and R may be any of the classes of radicals indicated in the several methods of preparation outlined; R may be any alkyl, aryl, aralkyl radical or hydrogen so that the formula represents any sulfhydryl compound.

Though the preparation of the modified resin and the method of recovering hydrogen sulfide and mercaptan from petroleum fractions have been described with only a few examples, the principles governing the preparation and the process are clear and the examples are to be considered simply as illustrative thereof.

What is claimed is:

1. A surface-modified resin having an exposed outer surface of amine radicals selected from the group of primary amino-groups and secondary amino-groups comprising the transesterification reaction product of .the surface layer molecules in particles of an acrylic resin selected from the group consisting of polymethyl methacrylate and polymethyl acrylate with an alkanolamine selected from the group consisting of monoalkanolamine and dialkanolamine, said reaction being carried out under transesterification conditions to cause the release of methyl alcohol as a by-product and said reaction being NHaRaSH carried out at a temperatur'e sufiicient to cause the methyl alcohol by-producttdvapo'rize from the reaction mixture.

2. A surface-mod ifiedfresin in accordance with claim 1 in which s'ai'd"expo s ed'outer surface comprises primary amino groups resulting from the reaction of said acrylic resin with a monoalkanolamine.

3. A surface-modified resin in accordance with claim 2 in which said monoalkanolamine is monoethanolamine.

4. A surface-modified resin in accordance with claim 1 in which said exposed outer surface comprises secondary amino-groups resulting from the reaction of said acrylic resin with a dialkanolamine.

5. A surface-modified'resin-in accordance with claim 4 in which said dialkano'lamine is diethanolamine.

6. A surface-modified resin having an exposed outer surface of secondary amino-groups comprising the transesterification reaction product of the surface layer molecules in a polymethyl methacrylate with diethanolamine, said reaction being carried out under transesterification conditions to cause the release of methyl alcohol as a by-product and at a temperature sufficient to cause the methyl alcohol by-product to vaporize from the reaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS 1,990,435 Hund Feb. 5, 1935 2,063,158 Greenewalt Dec. 8, 1936 2,138,762 Harmon Nov. 29, 1938 2,304,637 Hardy Dec. 8, 1942 2,363,581 Frosch Nov. 28, 1944 2,403,533 Kaszuba July 9, 1946 2,540,985 Jackson Feb. 6, 1951 2,579,492 Hansen et al. Dec. 25, 1951 2,568,747 Kirkpatrick Sept. 25, 1951 2,631,999 McMaster et al. Mar. 17, 1953 FOREIGN PATENTS 596,114 Germany Apr. 27, 1934 475,131 Great Britain Nov. 15, 1937 655,951 Germany v Jan. 27, 1938 OTHER REFERENCES Karrer: Organic Chemistry, Elsevier, 1938, pp. 112, 113 and 118. (Copy in Science Library.) 

1. A SURFACE-MODIFIED RESIN HAVING AN EXPOSED OUTER SURFACE OF AMINE RADICALS SELECTED FROM THE GROUP OF PRIMARY AMINO-GROUPS AND SECONDUARY AMINO-GROUPS COMPRISING THE TRANSESTERIFICATION REACTION PRODUCT OF THE SURFACE LAYER MOLECULES IN THE PARTICLES OF AN ACRYLIC RESIN SELECTED FROM THE GROUP CONSISTING OF POLYMETHYL METHACRYLATE AND POLYMETHYL ACRYLATE WITH AN ALKANOLAMINE SELECTED FROM THE GROUP CONSISTING OF MONOALKANOLAMINE AND DIALKNOLAMINE, SAID REACTION BEING CARRIED OUT UNDER TRANSESTERIFICATION CONDITIONS TO CAUSE THE REACTION BEING METHYL ALCOHOL AS A BY-PRODUCT AND SAID REACTION BEING CARRIED OUT AT A TEMPERATURE SUFFICIENT TO CAUSE THE METHYL ALCOHOL BY-PRODUCT TO VAPORIZED FROM THE REACTION MIXTURE. 